/*
 * Copyright (C) 2008 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.arlen.photo.photopickup.util;

import android.os.Handler;
import android.os.Looper;
import android.os.Message;
import android.os.MessageQueue;

import java.util.LinkedList;

/**
 * Queue of things to run on a looper thread. Items posted with {@link #post}
 * will not be actually enqued on the handler until after the last one has run,
 * to keep from starving the thread.
 * 
 * This class is fifo.
 */
public final class DeferredHandler {
	private LinkedList<Runnable> mQueue = new LinkedList<>();
	private MessageQueue mMessageQueue = Looper.myQueue();
	private Impl mHandler = new Impl();

	private class Impl extends Handler implements MessageQueue.IdleHandler {
		public void handleMessage(Message msg) {
			Runnable r;
			synchronized (mQueue) {
				if (mQueue.size() == 0) {
					return;
				}
				r = mQueue.removeFirst();
			}
			r.run();
			synchronized (mQueue) {
				scheduleNextLocked();
			}
		}

		public boolean queueIdle() {
			handleMessage(null);
			return false;
		}
	}

	private class IdleRunnable implements Runnable {
		Runnable mRunnable;

		IdleRunnable(Runnable r) {
			mRunnable = r;
		}

		public void run() {
			mRunnable.run();
		}
	}

	public DeferredHandler() {
	}

	/** Schedule runnable to run after everything that's on the queue right now. */
	public void post(Runnable runnable) {
		synchronized (mQueue) {
			mQueue.add(runnable);
			if (mQueue.size() == 1) {
				scheduleNextLocked();
			}
		}
	}

	/** Schedule runnable to run when the queue goes idle. */
	public void postIdle(final Runnable runnable) {
		post(new IdleRunnable(runnable));
	}

	public void cancelRunnable(Runnable runnable) {
		synchronized (mQueue) {
			while (mQueue.remove(runnable)) {
			}
		}
	}

	public void cancel() {
		synchronized (mQueue) {
			mQueue.clear();
		}
	}

	void scheduleNextLocked() {
		if (mQueue.size() > 0) {
			Runnable peek = mQueue.getFirst();
			if (peek instanceof IdleRunnable) {
				mMessageQueue.addIdleHandler(mHandler);
			} else {
				mHandler.sendEmptyMessage(1);
			}
		}
	}
 }
